This invention relates to a device and method of suppressing fire plumes above combustible structures. More particularly, the present invention relates to controlling and suppressing fires by inserting a catalytic screen into the fire and diverting the reactions from the violent flame zone to a silent catalytic solid surface.
When a flaming combustion starts, the hot flame above the burning object acts as an aerodynamically strong diffusion pump powered by natural buoyancy forces. Ambient air is entrained along the boundary of the flame because of the upward movement of hot combustion gases caused by the large buoyancy forces. The violence of the fire thus depends on the buoyancy force generated by hot gases rising above the fire and the ambient air rushing into the fire. More often than not, crosswinds augment the fire violence. In time, the flame turns into a propagating large-scale fire with ever increasing strength and ability to destroy nearby combustible objects. Out of control fires cause severe threats to both life and property at an ever increasing rate. Thus, a critical need exists for newer and more efficient fire control methods.
Current methods used to suppress fires of various magnitudes include cooling the fire by water mist, blanketing oxygen influx by using heavy gases such as carbon dioxide and foam, and inhibiting chain-branching chemical reactions in the flame by using chemical additives. Chemical additives include, but are not restricted to, the halons CF2Br2 and CF2BrCl, and certain dry powders. Additionally, some explosive reactions are used to aerodynamically blow off the flame and assist in suppressing the fire.
The degree of success achieved in these methods depends on the specific fire scenario at hand. The prior art methods are known to present serious limitations under various fire scenarios. For instance, the water spray methodology of controlling fires is the most widely used, but the water mist is often incapable of penetrating against the upward fire flow into the surface to cool the fire. In addition, chemical additives are not always effective, and they pose pollution problems that may be caused by their use in controlling fires. Therefore, suppression of wild fires and uncontrolled fires generally continues to be difficult, especially for very violent fires of great strength having strong upward flow of hot combustion gases.
Some attempts have been at using some type of screen or mesh covering inside fire plumes to assist in controlling fire. However, previous studies reporting the effect of including non-catalytic screens inside fire plumes indicate that screens provide little assistance in suppressing a flame. In a journal article, T. Log and G. Heskestad, Fire Safety Journal, volume 31, 1998, describe variations of flame properties upon introducing a non-catalytic metal screen into the flame. The authors report a net increase in time-averaged flame temperatures. The placement of an inert surface inside a flame did not change the overall chemistry and dynamics of the flame.
U.S. Pat. No. 5,158,144 issued to Mark D. Shaw and Laurence M. Bierce on Oct. 27, 1992 teaches a method of creating a non-burning zone at the flame base by introducing a non-catalytic metal mesh or screen. By constantly raising the screen, a distance of free flowing fuel without fire can be created below the flame. The screen thus prevents the fire from burning below it mainly due to the aerodynamic effect. However the screen does not modify the properties of the flame burning above the screen.
Accordingly, it would be highly desirably to provide a method for using a screen or mesh for suppressing fire that would modify the flame properties such that the flame would be easily extinguished.
Certain combustion catalysts are known to create reactive surface sites by significantly reducing the activation energy of combustion reactions. Several theories have been proposed for the combustion and ignition of hydrocarbon fuels in the presence of noble metal catalysts as early as the 1970s and 1980s. The catalytic ignition behavior of a fuel- air system depends on the nature of catalysts, their effective surface area, and fuel-air equivalence ratios.
Applications for catalytic combustion technology exists in several camping accessories, household appliances and industrial combustion systems. In these existing applications, catalytic combustion technology is used to replacing flaming combustion with catalytic radiant glow to create flameless combustion applications for cooking, heating, and improving efficiency. However, prior art does not exist with respect to the application of catalytic combustion technology for suppressing and controlling violent fires.
The inventor has found that flaming gas phase combustion will transition to glowing surface combustion in the presence of a significantly lower activation energy catalytic surface. In the present invention, a fire is controlled by transforming the gas phase combustion of a violent flame into a surface catalytic combustion process, thus weakening or eliminating the violent fire plume above the burning structures.
The gas phase ignition temperature of a combustible mixture containing a gaseous fuel and air is generally above 1000xc2x0 C. However, in the presence of a suitable catalytic surface, the fuel-air mixture can ignite at a much lower temperature because of lower activation energy of combustion. The ignition temperature can be as low as 400-500xc2x0 C. depending on the nature of the catalyst. When the catalyst is heated to above its activation temperature, combustion reactions occur on the surface, resulting in a glowing surface. As the surface combustion becomes more efficient, the flame above the burning surface becomes weaker and unstable. At high enough catalytic combustion rates, the flame will disappear and leave behind a glowing surface, thus preventing the fire from propagating to nearby structures. Because of the near absence of a strong fire plume above the burning objects, a conventional sprinkler system can be easily used to cool the surface.